1. Field of the Invention
The present invention relates to a chip on tape package and more particularly concerns an arrangement for protecting the fragile leads of the package and for facilitating alignment during assembly of the die to the laminated tape.
2. Description of Related Art
A TAB (tape automated bonding) package, sometimes termed a chip on tape package, is one of several methods of assembling an integrated circuit die or chip to a plurality of conductive leads so as to allow the chip to be electrically connected to other components, such as conductive pads on a printed circuit board for example. The TAB package frequently comprises a section of a thin laminated tape formed of a thin layer of substrate and a layer of thin conductive leads bonded thereto with an opening, generally of rectangular configuration, to mate with the rectangular configuration of a die. The die is positioned substantially in the tape opening, and its connector pads are bonded to ends of the leads of the laminated tape that extend inwardly of the tape opening to overlay the respective conductive pads of the die to which they may be bonded by conventional automatic bonding techniques. The conductive leads of the tape extend laterally outwardly of all four outer sides of the tape section and also project downwardly below the tape section and die, being configured and arranged for resting upon and electrically contacting contact pads formed on another electrical component, such as a printed circuit board (PCB) for example. The laterally outwardly and depending free ends of the tape are bonded to the conductive pads of the printed circuit board for physical and electrical connection by conventional techniques, and hold the tape section and die spaced above the PCB.
In assembly of the tape to the die, the inner end of the tape leads must be precisely aligned with the die pads before bonding. This alignment has been carried out in the prior art either manually or visually, or by use of external alignment devices. Further, the assembly of die and tape, e.g. the TAB package, must be handled and shipped as a separate article, and is often assembled to other electrical components or a printed circuit board by automatic pick-and-place machines.
As more and more electronic functions are packaged within smaller and smaller packages, components, contact pads, and electrical leads all become increasingly smaller. Frequently the conductive leads of the TAB package have widths on the order of 0.002 inches and are spaced from one another by like distances. The thickness of the leads are even smaller than their 0.002 inch widths and spacing. These leads are generally made of copper, and extend freely and totally unsupported beyond the outer edges of the thin laminated tape. Consequently they are highly susceptible to bending, breaking and other types of damage. These fragile free leads are not only easily damaged by inadvertent contact with other objects, but sudden accelerations to which the TAB package may be subjected can also result in bending or distortion of the leads. Shipping of TAB packages is also difficult and inconvenient, often being carried out in complex carriers or on reels.
Die alignment is typically accomplished by external alignment devices, either visually or manually, which complicates production and assembly, and requires increased labor. Arrangements for protecting the TAB package leads for surface mounting have required separate and independent supporting devices. In some arrangements a hole is formed in the printed circuit board directly below the face of the die and a soft support is inserted into the hole to support the die during attachment of a heat sink. In the prior art, if a heat sink is used, it is attached to the die after the TAB package has been mounted on the PCB. In the attachment of a heat sink to the opposite side of the die, some pressure must be exerted against the die and therefore against the printed circuit board through the very fragile free leads, which are not capable of supporting any significant amount of pressure.
Prior solutions to these problems have addressed one or more, but not all of these problems. These solutions often require more area on the printed circuit board, require more parts and are difficult or virtually impossible to automate.
Accordingly, it is an object of the present invention to provide for mounting, alignment and protection of leads of a TAB package by methods and structures that avoid or eliminate above mentioned problems.